Precision alignment accuracy in a sub-micron scale, together with high unit-per-hour (UPH), has always been a huge challenge in the electronics and semiconductor industry in the past a few decades. On the other hand, the demand for an alignment metrology with both high-precision and high UPH is significantly increased due to applications in 3-D integration, optical packaging, advanced wafer-level packaging, microfluidics, MEMS, and NEMS.
Either an optical microscopy, or an IR transmission microscopy, or an intersubstrate microscopy is used in conventional alignment methods to monitor the alignment marks on both wafers or chips during the alignment process within an aligner and/or a bonder. In order to match the alignment marks on both wafers or chip-and-wafer, one of the two components, usually the one held by the bond head, can be adjusted in x, y, and z directions and rotated in theta. Once the alignment markers are aligned, the microscopy is removed, the component on the bond head is then brought down to the wafer on the bottom chuck for bonding. Both wafers (or chip and wafer) are not in contact during the alignment process and consequently there is no force in between the two components to hold the alignment accuracy, which can be dramatically reduced during moving the component on the bond head down to contact the wafer on the chuck and then bonding process.
The present invention is distinguished from conventional alignment methods in that the two components (either wafer to wafer or chip to wafer) are in contact during the active alignment process assisted by magnetic force between complimentary pairing patterned magnets on two components in an applied magnetic field. Once the alignment process is done, both components are locked in-situ by the magnetic force without further alignment accuracy loss. A novel bonding method is then used to obtain vertical interconnects between the two components without losing the alignment accuracy, which is described in another invention by the authors. In the case of chip-to-wafer bonding, all chips can be placed on the wafer with loose alignment accuracy with high throughput. The force between pairing patterned magnets will push for the high precision alignment via self-alignment process. At some particular cases, high-precision alignment can be done between the chips and the wafer at the same time via external activation of self-alignment between the patterned magnets by turning on the external magnetic field. Thus a high-precision alignment method with high UPH is achieved. Since the magnetic force will hold the alignment together between the chip and the wafer, the bonding can be done at once for all the chips after the chips have all been aligned. By doing so, we can also cut down the UPH time for chip-to-wafer bonding.